Variable frequency u. h. f. coaxial oscillator



April 9, 1957 w, TODD 2,788,448

VARIABLE FREQUENCY U.H.F. COAXIAL OSCILLATOR Filed Dec. 7, 1955 f g N .4 I'

O l"l l1' gl f. N 'n co Z l A i INVENTOR S w/LL/AM Toon l l BY o A Marn-rgb In Arma/gy VARIABLE FREQUENCY U. H. F. COAXIAL OSCILLATOR William Todd, Interlaken, N. J., assignor to the United States of America as represented by the Secretary of the Army Application December 7, 1955, Serial No. 551,713

4 Claims. (Cl. Z50-36) (Granted under Title 35, U. S. Code (1952), sec. 26@

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to ultra-high frequency oscillators and, more particularly, to an arrangement for tuning a coaxial line resonator particularly adapted for operation with tubes commonly referred to as grounded-grid type tubes.

Coaxial line type resonators are customarily employed for determining the output frequency in oscillators utilizing pencil-triode type tubes such as the 5675. The cathode and anode circuits may be tuned by means of shortcircuiting plungers in direct sliding contact with the cathode or anode stud terminal to provide shorted quarterwavelength lines. In operating such oscillators, it has been found that the output frequency is very sensitive to adjustments of the anode plunger because of the dificulty in maintaining proper contact. In addition, simply tightening the anode or plate plunger lock nut is usually sutiicient to cause an error in the desired output frequency. Moreover, for satisfactory tuning, Vernier tuning mechanisms are additionally required and such mechanisms usually require critical adjustment for wide range tuning. Such critical adjustments can very easily cause tube breakage due to the close mechanical tolerances involved in the above Vernier and the accidental overtravel in making such an adjustment. Tube breakage in such devices is also likely to occur when the tube is replaced due to the mechanical stress imposed upon the glass seal by reason of the torque produced by any eccentric positioning, and the spring pressure of the plunger contact ingers. Also, in such devices, replacement of the tubes will sometimes cause the plunger contact fingers to be bent or broken. Furthermore, the short length of the anode stud limits the tuning of the device to a very narrow range.

It is therefore an object of the present invention to provide a coaxial line tuner wherein the above-mentioned limitations are completely eliminated.

It is another object of the invention to provide a coaxial resonator type tuner capable of being tuned linearly over a relatively wide range of frequency and which is free from any critical adjustments.

It is still another object of the invention to provide an anode or plate line coaxial resonator type variable tuner wherein interlocking adjustments are minimized.

It is still another object of the invention to provide an anode or plate line coaxial tuner wherein the tube breakage problem is eliminated.

In accordance with the present invention there is provided a means for tuning a coaxial line resonator which is electrically open circuited at both ends. It includes a dielectric plunger disposed between the inner and outer conductor of the coaxial line and whichis in contact with the inner surface of the outer conductor. By axially positioning the plunger within the line, the effective electrical length thereof is varied. In a specific embodiment of the invention, there is included a dielectric spacer aixed at ted States Patent one end of the coaxial line between the inner and outer conductors thereof and the dielectric plunger is provided with an axial bore which is adapted to telescope the inner conductor when the plunger is axially positioned within the coaxial line.

For a better understanding of the invention together with further objects thereof, reference is had to the following description taken in connection with the accompanying drawing in which:

Fig. 1 shows an embodiment of the invention utilized in an oscillator circuit, and

Fig. 2 is a section taken along the lines 2-2 of Fig. 1.

Referring now to the drawing, at 10 there is shown a coaxial resonator structure forming the anode or plate line resonator of a grounded grid oscillator utilizing a pencil type triode 12. The plate or anode terminal of triode 12 is terminated in a cylindrical sleeve 14 centrally positioned within a cylindrical member 16 which forms an integral part of outer conductor 18 of coaxial resonator 10. Cylindrical member 16 comprises the iixed or untuned section of resonator structure 10 and is terminated at one end by an inwardly extending ilange 20 and at the other end by an outwardly extending flange 22. As shown, flange 22 is spaced and insulated from a metallic ring 24 which is connected to the grid (not shown) of triode 12. The cathode tuning structure to the right of grid ring 24 is a conventional coaxial cathode tuned circuit which is well known in the art and no further description thereof is believed necessary.

Anode sleeve 14 is disposed within a metallic cylindrical receptacle 26 having fingers 28 at one end thereof which are in contact with the outer surface of sleeve 14. The other end of receptacle 26 is terminated in a conductor 30 which forms the central conductor of the tunable section 31 of coaxial resonator structure 10. As shown, a xed dielectric spacer 32 is provided between inner conductor 30 and outer conductor 18, the spacer being arranged so that it abuts the base of receptacle 26 and a surface of flange 22 to provide one termination of tunable section 31. A direct current potential may be applied to the plate of pencil triode 12 by means of spiral- 1y wound wire as at 34 imbedded in the free surface of spacer 32 and having one end atiixed to outer conductor 18 and the other end afiixed to inner conductor 30. Such spiral wire provides a means of supplying power to the anode of the tube without appreciably affecting the flow of radio-frequency currents in the line. If desired, a second ixed dielectric spacer (not shown) may be disposed adjacent spacer 32 within coaxial resonator structure 10 between outer conductor 18 and inner conductor 30 to maintain wire 34 in position. Also disposed intermediate inner conductor 30 and outer conductor 18 is dielectric plunger 36 made of teiion or any other suitable dielectric material having a dielectric constant greater than unity, and which is provided with an axial longitudinal bore 38 extending partially therethrough. The diameter of bore 38 is made slightly greater than that of inner conductor 30 and plunger 36 is positioned so that axial movement thereof will cause bore 38 to telescope conductor 30. As shown, plunger 36 consists of a head portion 42 having a screw thread of prescribed pitch on the outer periphery thereof adapted to engage a corresponding screw thread provided on the inner periphery of outer conductor 18, and an axial shaft portion 44 of reduced diameter, Shaft portion 44 is aiiixed to a metal shaft 50 by any suitable means. Shaft 50 may be rotatively driven by any suitable device to control the axial movement of plunger 36 within coaxial structure 10. The axial movement of head portion 42 is limited at the end remote from receptacle 26 by means of a suitable adapter 52 which is provided with a threaded iiange portion adapted to engage a corresponding threaded portion on the outer surface of conductor 18 provided therefor. Spacer 32 provides the stop for head portion 42 at the other end of tunablesection 31.

In operation, as the shaft 50 is rotated the amount of insertion of plunger head portion 42 within tunable section 31 is varied to change the effective dielectrical constant of the insulation between the inner and outer conductors of section 31, and hence effectively vary the elec trical length of the line. Since the `ends of tunable section 31 are thus effectively terminated by a dielectric, it is in effect an open half-wave length line or integral multiple thereof, whose electrical length is varied by the insertion of dielectric plunger 36 to tune the coaxial plate line. It is to be noted that bore 38 may be made of such length that when threaded head portion 42 of plunger 36 abuts the free surface of spacer 34, a major portion of inner conductor 30 will be within the bore 38, and when the threaded portion 42 hits the inner wall of flange adapter 52, the free end of inner conductor 30 is substantially aligned with the open end of bore 38.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a radio frequency oscillator circuit wherein the output frequency is a function of the effective electrical length of a coaxial line resonator having its center conductor connected to the anodemovfwthe oscillatorwtubq means for varying the effective electrical length of said line comprising a dielectric spacer aixed between the center and outer conductor at the anode end of said coaxial linc, a dielectric plunger disposed between said center and outer conductor and having its outer periphery in contact with the inner surface of said outer conductor, and means for axially positioning said plunger relative to said spacer.

2. The device in accordance with claim l wherein said plunger includes a head portion disposed opposite said spacer and having its outer periphery in engagement with the inner surface of said outer conductor, a shaft portion radially spaced from said inner surface and an axial bore adapted to telescope said center conductor when said plunger is axially positioned within said line.

3. A tuner ,for a coaxial line resonator comprising a dielectric spacer afxed between the inner and outer conductor of said line at one end thereof, a spirally wound wire imbedded in one surface of said dielectric spacer with one end of said wire connected to said outer conductor and the other end of said wire connected to said inner conductor, a dielectric plunger disposed between said inner and outer conductors and having its outer periphery in contact with the inner surface of said outer conductor, and means for axially positioning said plunger relative to said spacer to vary the electrical length of said line.

4. The device in accordance with claim 3 and further including an axial bore within said plunger and adapted to telescope said inner conductor when said plunger is axially positioned within said line.

References Cited in the file of this patent UNITED STATES PATENTS 2,502,531 Morton et al. Apr. 4, 1950 

